Thin film inductors are one of the possible solutions for future microprocessor power conversion needs. To efficiently convert power, inductors should be designed with low loss and a high quality factor, Q. In addition, for many applications, it is important for the inductor layout area to be small to save silicon space, while providing large power storage per unit area. Inductors are typically formed as planar structures on top of semiconductor substrates having planar metal layers patterned in a spiraling manner in order to create multiple turn inductive windings. One disadvantage to planar inductor designs in that the windings generally form relatively low Q circuits. Moreover, increasing the amount of turns required more silicon area, which reduces the amount of silicon area available for other devices and wiring.
One way of increasing the Q of an inductor is by wrapping a ferromagnetic core around the coils of the inductor. The ferromagnetic material enables the inductor to store more energy for a given current, and therefore increases power that can be delivered for a given resistance loss. However, the magnetic fields in the ferromagnetic material are limited by saturation. Saturation places a limit on the maximum current, and therefore limits the maximum power that the inductor can support.